Comparing tree-ring and pollen climate reconstructions in a central region of the Italian Alps

When approaching multi-proxy climate reconstructions, the selection of appropriate climate-sensitive records is a crucial step for assessing past climate variability. Both tree-ring and pollen-stratigraphical records have their own time resolution and they typically cover different time lengths. Tree rings allow annually-resolved reconstructions, however dendrochronological records rarely exceed 4-5k years and only few records cover the whole Holocene, whereas pollen records show variable time resolutions but go much further back in time. When comparing the variability of these two proxies it is therefore necessary to select a common period and to adjust the annually-resolved resolution of tree rings records to the generally lower and variable resolution of the pollen ones. A first comparison between two quantitative summer temperature reconstructions derived from tree-ring and a high-resolution pollen record (~9 years for the last 200 years) was performed in the central region of the Italian Alps. An area of approximately 150 km of diameter was selected, comprising the pollen-stratigraphical record of Lake Lavarone (Trento), base for the quantitative pollen-inferred reconstructions, and tree-ring series of European larch (Larix decidua Mill.), Swiss stone pine (Pinus cembra L.) and Norway spruce (Picea abies Karst.) from 42 sites located in five mountain groups: the Silvretta Group (Switzerland), the Ötztaler-Venoste Alps (Austria, Italy), the Bernina Group (Switzerland, Italy), the Ortles-Cevedale Group (Italy) and the Adamello-Presanella Group (Italy). Both the tree-ring and the pollen-based reconstructions were previously calibrated using the modeled site-specific instrumental temperatures from an improved version of the dataset of Brunetti et al. (2006). The two independent summer temperature reconstructions, after adapting the tree-ring series to the varying time resolution of the pollen series, showed a correlation of +0.77 over the common period 1803-2003, thus opening the possibility of performing integrated multi-proxy climate reconstructions including more sites from the whole arch of the Italian Alps. Currently, the comparisons are being developed including tree-ring records from the whole Alpine arch and the pollen-stratigraphical records available in northern Italy, that could cover the last 200 years, or part of this interval, and have a good time resolution.